(CNN) - The American opioid crisis is only part of an overall drug abuse emergency. Cocaine-related overdose deaths among non-Hispanic blacks are on par with overdose deaths caused by heroin and prescription opioids among whites, according to a study published Monday in the medical journal Annals of Internal Medicine.

"Numerous US national surveillance studies and media reports have highlighted an alarming rise in drug poisoning deaths in recent years," said Meredith Shiels, a co-author of the study and an investigator at the National Cancer Institute. However, most of the studies focus on opioid-related deaths, including prescription painkillers, heroin and fentanyl. They also tend to emphasize the fact that death rates are "rising most rapidly among white Americans," she said.

The researchers, from the National Institute on Drug Abuse and the National Cancer Institute, found that cocaine overdoses also killed Hispanics and whites over the time period studied.

But the new study reveals the increasing rates of drug overdose deaths among black and Hispanic Americans.

"These increases have received less attention," Shiels said.

Overdose deaths rise 5.5% each year

According to the US Centers for Disease Control and Prevention, 16,849 Americans died due to an overdose in 1999, and in 2015, the number of overdose fatalities reached 52,404. Overall, rates of overdose deaths increased by 5.5% per year between 1999 and 2015. Most of that increase has been attributed to opioid-related deaths among white persons.

To understand drug trends in fatal overdoses, the researchers looked at data from 2000 through 2015. National statistics on drug overdose deaths are based on information from death certificates.

Increases in overdose deaths were seen across all age groups of whites and Hispanics, yet rising rates were most pronounced among older black men (50 or older) and older black women (45 or older).

Cocaine was the largest contributor to overdose deaths among black men and women. Cocaine-related deaths peaked between 2004 and 2007, declined between 2008 and 2011, and then increased again between 2012 and 2015 among blacks, whites and Hispanics. But, the largest recent increase in overdose deaths for black and Hispanic people was due to heroin.

However, Shiels said, there were also increases due to natural or semisynthetic opioids (such as morphine and oxycodone), benzodiazepines (such as Valium and Xanax), synthetic opioids (such as fentanyl) and psychostimulants (such as methamphetamine) among blacks and Hispanics.

"There were too few drug overdose deaths among Asian-Americans to be able to draw meaningful conclusions about mortality rates by drug type, so this group was omitted," Shiels said.

The researchers also compared data from 2000 through 2003 with data from 2012 through 2015. Among blacks, total overdose death rates increased from 6.1 per 100,000 people for the earlier period to 9 per 100,000 people for the later period; among Hispanics from 4.2 per 100,000 to 6 per 100,000; and among whites from 5.6 per 100,000 to 15.5 per 100,000.

"In the most recent years studied, 2012 to 2015, cocaine overdose deaths were almost as common in black men as prescription opioid deaths in white men and slightly more common in black women than deaths from heroin overdose in white women," Shiels said.

The percentage of overdose deaths not attributed to a specific drug (as recorded on death certificates) between 2000 and 2003 and 2012 and 2015 varied across groups: 14% and 16%, respectively, for black people; 14% and 16%, respectively, for Hispanic people, and 25% and 21%, respectively, for white people.

Overall, about 20% of death certificates reporting an unintentional overdose are missing information about the drug that caused the death, the researchers said.

'Widely available' drugs

"Drug poisoning deaths can be classified as unintentional, suicide, homicide or undetermined intent," Shiels explained. "As unintentional poisonings make up the vast majority of poisoning deaths (about 80%), it is likely that some of the deaths classified as 'undetermined intent' are also unintentional overdoses."

These blurry lines mean the total number of fatal overdoses may be underestimated across the United States, she said.

Though correctly estimating cause of death may be a challenge, it is less difficult to explain the increase in fatal overdoses.

"The rise in prescription opioid overdoses is clearly related to the rise in availability of prescription opioids in recent years," said David Thomas, a co-author of the study and a health scientist at the National Institute on Drug Abuse.

"Compounding the problem, heroin is widely available and much less expensive on the black market than diverted prescription opioids, thus many prescription opioid abusers are switching to heroin because of price and availability," he said.

Adding to these problems, fentanyl and carfentanyl are also being sold on the streets as heroin. These two drugs "are hundreds or thousands of times more powerful than heroin," Thomas said.

The reason behind the increase in cocaine use is not as clear. Still, the rising rate of overdoses caused by that drug "does underscore that we not only have an opioid crisis but a more general drug abuse crisis," Thomas said.

This opinion is shared by Brandon DL Marshall, an associate professor in the department of Epidemiology at the Brown University School of Public Health.

'Alarming' increase in fatal overdoses

Marshall, who was not involved in the new research, said it draws attention to the fact that the drug crisis is affecting all communities, "regardless of racial/ethnic background."

"While overdose death rates are highest among non-Hispanic whites, the increase among African-Americans and Hispanics is alarming and deserves greater public health attention," he said.

What's new in the study is how the different races had different peak ages for overdose deaths, Marshall noted. The highest rates for whites were in the 30-to-34 group, while the highest rates for blacks are among the 50-to-59 group.

"More research is needed to uncover the underlying reasons for this difference by age and race," he said.

Marshall also noted that, due to a lack of information about specific drugs causing an overdose on death certificates, the study was not able to clarify whether the uptick of overdose deaths in recent years is due entirely to opioids or other drugs.

One unrelated recent study looked at the underreported drug information on US death certificates and found that in 2008, 25.4% of the total 36,450 fatal overdoses did not identify a specific drug, compared with 19.5% of the 47,055 overdoses in 2014, he said. Some states provided specific drug data for 99% of all fatal overdoses, but other states did so only 50% of the time.

"States with centralized systems in which medical examiners are responsible for investigating overdoses have higher rates of reporting toxicological results on death certificates than de-centralized, county systems in which coroners investigate deaths," Marshall said, based on his knowledge of a separate 2013 study.

"The difference may be due to the fact that coroners are typically non-physicians who have less familiarity with toxicological analyses and terminology," he said.

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